This application is based on and claims priority from Japanese Application No. HEI 3-144300 filed Apr. 1, 1991, the disclosure of which is incorporated by reference herein.
The present invention relates to a zoom lens system, and more particularly to a two-group zoom lens system for a power zooming monitor.
Standard zoom lens systems which have a focal length coverage from the wide-angle end to a sub-telephoto end are generally composed of two lens groups, a negative first lens group and a positive second lens group, as arranged in order from the object side. The diaphragm stop in such standard lens systems is customarily disposed either ahead of or within the second lens group so that it moves in unison with the second lens group upon zooming.
Such conventional zoom lens systems are sometimes designed as power zoom lenses which have a lens drive motor built in the lens barrel to achieve zooming. In this case, however, the motor is inevitably disposed outside the diaphragm stop, thereby increasing the diameter of the lens barrel.
Unexamined Published Japanese Patent Application No. 266511/1987 discloses a zoom lens system for use with video cameras that has a fixed diaphragm stop disposed between the first and the second lens groups. However, this lens system which uses a fixed diaphragm stop suffers from the disadvantage that deleterious flare rays of light are produced upon zooming.